ELAC Technische Software CARA 2.0 computer program

I have been a proponent of methodical modeling and room analysis as aids in setting up audio systems and rooms. They work hand in hand: Modeling predicts a feasible room arrangement, and analysis, along with careful listening, determines how close the outcome is to that predicted. Of course, there should always be another round of modeling to see if the current setup can be improved with more work. The spiral continues, toward, one hopes, perfection.

Modeling is of particular importance: I like to know whether a room rearrangement is likely to be effective before I try to persuade my wife to agree to it—no sense using up my allowance on likely failures. Besides, moving heavy objects around is not my idea of fun. Until recently, I've used RPG Diffuser Systems' Room Optimizer software as a guide to speaker placement, room arrangement, and room treatment. Room Optimizer lets me define room dimensions and some speaker parameters before it goes about optimizing placement and suggesting needed room treatments.

I enjoy watching the little icons representing the speakers and the listener jump around onscreen as the software assesses one position after another. The results have been worthwhile, especially for my multichannel setup, which lives in a too-regular rectangular space. On the other hand, my main system lives in an L-shaped room; Room Optimizer works only for rectangular rooms.

The solution was to use another program, CARA 2.0 ("CARA" stands for Computerized Acoustic Room Analysis), made by ELAC Technische Software GmbH. This is a much more complex system requiring lots of effort and computer resources, but both can be justified.

To use CARA, one first creates a full three-dimensional model of the listening room, using the program's CARACAD module. By "full," I mean that all room dimensions and surfaces are defined: doors, windows, furniture, soffits, bays, etc. The placement, dimensions, and materials making up these elements determine how they will absorb, reflect, and/or diffuse sounds of different frequencies. CARA provides a library of the basic room elements and furniture one might find in a listening room or recording studio, and includes CAD tools for constructing others from a bill-of-materials list. In addition, CARA offers specific and helpful tutorials on modeling such things as L-shaped rooms, curved surfaces, sloped and false ceilings, and other architectural features.

The effort required to do all this is considerable; for reasons stated below, I ended up creating three room models of increasing detail and complexity. Especially fascinating and useful was a program utility that lets you look into and walk around the virtual room to confirm that it does, indeed, look like the real thing.

Next, using CARA Loudspeaker Editor, you build models of your speakers. If you're lucky, you'll find your speaker in the library of +150 models provided. Although most of the brands are European (ELAC of course, and Burmester, Canton, JMlab, etc.), some models from Infinity and JBL are included. I had to create my own models of the Revel Ultima Studios from engineering drawings and specifications found at Revel's website. The model tells CARA about the speaker's specific radiation characteristics and any details, right down to the height of the floor spikes, that affect the results. (By contrast, Room Optimizer provides only generic speaker types.)

Finally, place speaker models and listener in the room model using x, y, and z coordinates, and angular orientation with respect to a reference line. In addition, you set spatial and angular limits for the range of positions to be tried. CARA can accommodate setups of two, three, four, or five speakers, with or without subwoofer(s).

At this point, you might expect, as I did, that it would be a simple matter of hitting "GO" and letting CARACALC do its thing. But due to the program's power and complexity, you should first set goals (or end-points) in terms of frequency-response linearity, imaging, etc. I found these criteria somewhat nebulous despite the numerical precision of the guide numbers, but they did reflect the graphed results, which I found more useful. In addition, CARA determines the effect of reflections at every boundary from each source at every possible position. This requires a lot of computation; using full detail in the models and six or more reflections might take weeks of computer time!